Rubber hose with braided steel wire reinforcement is used extensively in hydraulic circuits because of its high burst strength. Such hose is conventionally furnished with an elastomeric core tube, one or more plies of the braided reinforcement, depending upon the diameter of the hose and the required burst strength, and an elastomeric cover. In general, it has been the practice in the industry to use a plurality of fine wire filaments to form strands and to weave the strands into a braid wherein each strand alternatively crosses over and under two other strands, the strands being woven spirally in right and left hand directions over a rubber core tube. When two or more plies of braided wire reinforcement are used, there is usually a thin rubber liner between the plies to provide stress transfer from the inner ply to the outer ply.
In conventional braided wire reinforced hose, the wire diameter is kept relatively small in order to retain acceptable flexibility of the hose, minimum hose O.D. relative to the I.D., and to facilitate gripping of the hose by couplings. Typically, a conventional hose of 1/2" I.D. for meeting SAE 100R2 requirements has two ply strands which consist of eight 0.012 inch wires in a braid that are woven in a manner to provide about 80% coverage of the core tube. With steel wire of 350,000 psi wire tensile strength the burst strength of such a hose is about 15,000 psi.
In the past, attempts have been made to produce hose with a single ply wire braid that would meet performance requirements of two-braid with the object of reducing costs through the use of a lesser total weight of wire and a smaller O.D. for a given I.D. to correspondingly reduce coupling size. One approach to achieve two-ply performance with a single ply is to use wires of greater diameter, as for example, using strands made up of five wires or filaments of 0.020 inch diameter in place of eight wires of 0.012 inch diameter for 1/2" I.D. hose. In such case, the one-ply of reinforcement with the thicker wires provides as much burst strength as two-ply reinforcement with finer wires, but the hose flexibility is reduced to an unacceptable level. Also, greater difficulty has been experienced in gripping the hose with crimp-type couplings similar to those shown in U.S. Pat. No. 2,535,460, so as to provide satisfactory impulse test results without leakage at the couplings.
In another attempt disclosed in U.S. Pat. No. 3,463,197 the wire diameter has been reduced over conventional practice, the number of wires per strand has been increased, and the strands are woven so as to crowd and overlap each other so that the wires bunch up into two or three layers and so that 100% coverage of the core tube is achieved. However, because of the crowding and bunching of the large number of fine wires in each strand it has been found difficult to apply the braid to the core tube without having wires crossing each other where they should be lying next to and parallel to each other. Inconsistent and poor impulse test results have been experienced with such hose and it is believed that this is at least in part due to such cross-overs.